1. Field of the Invention
The present invention relates generally to the field of antennas, and more particularly to a low profile antenna system for a card-like communication receiver.
2. Description of the Prior Art
Card-like communication receivers, such as credit card paging receivers have become popular in many countries throughout the world. However, because of their limited size, especially in their thickness, it has often been a problem to provide an effective antenna. One solution to the antenna problem has been to use the plates forming the front and rear covers of the card-like receiver as the conductive elements of a loop antenna. While this solution produced a functional loop antenna, additional complication in the design was encountered due to problems in coupling the plates to the printed circuit board supporting the receiver circuitry while continuing to allow access to the inside of the housing.
Because the aperture of the loop antenna formed by the front and rear cover plates is relatively small, other solutions were proposed to improve the performance of the loop antenna. One such solution was to provide a slot antenna which was integrated with and formed a part of the housing of the card-like receiver.
Because most prior art antennas for card-like communication receivers utilized a loop antenna, receiver sensitivity was generally good when the receiver was positioned on the body due to well known body enhancement effects, however, receiver sensitivity was generally significantly degraded when the card-like receiver was removed from the body, such as when set on a desk. One solution for providing improved receiver sensitivity off the body was to provide a center-fed antenna loop into which was interposed a dielectric. Such an antenna functioned as a loop antenna when the card-like receiver was carried on the body, and acted as a dipole antenna when the card-like receiver was removed from the body. While providing the performance improvements, such an antenna was generally more suitable for use at lower receiver operating frequencies.
As a result, what is needed is a receiving antenna for a card-like communication receiver operating at higher receiver operating frequencies, such as at 930 MHz, and which provides good sensitivity when worn on the body, and also good sensitivity when removed from the body.